The present invention relates to a sintered self-lubricating article prepared by powder metallurgical method and particularly to a sintered self-lubricating article usable as lubricating elements at elevated temperatures near 300.degree. C without assistance of any other lubricant e.g. oil or grease.
In the prior art, bronze-graphite sintered article is conventional and commonly used as a sintered lubricating article.
However, these sintered lubricating articles are disadvantageous in that they are not safely usable as self-subricating elements without assistance of suitable lubricant e.g. oil or grease and/or at elevated temperatures near 300.degree. C.
This is because when used under such severe conditions, each component of the article is inevitably highly oxidized, resulting in growth (dimensional change) by heat to cause remarkable drop of wear resistance or mechanical strength or the like. Such degradation of properties of a lubricating article comprising e.g. a bush type sintered element results in change of diametrical size and thus clinging to a shaft, to cause extraordinary wear, while oxidation of graphite and production of metal oxide causes increase in wear coefficient and damage of a shaft, as well as fructure and cracks due to drop of mechanical strength.
It has been found that these disadvantages in the prior art can be eliminated by a sintered self-lubricating article according to the present invention, said article having great oxidation resistance, high dimension stability and high wear resistance at elevated temperature without assistance of any other lubricants and consisting essentially of 5 to 10 percent by weight of tin, 8 to 40 percent by weight of zinc, 5 to 15 percent by weight of graphite and the balance being copper.
It is one of the most important properties for a self-lubricating article used in the absence of any lubricant e.g. oil or grease, namely, under a so-called dry lubricating condition, that solid lubricating film is sufficiently formed or an excellent film-forming property is provided.
The said solid film contributes to improvement in wear resistance and seizure resistance of the said article.
According to the present invention, it has been found that a sintered article including more lithium fluoride is remarkably improved in film-forming property thereof.
Accordingly, the present invention also relates to an improvement in film-forming property of a sintered self-lubricating article.
In the sintered self-lubricating article according to the invention as described above, said article further contains less than 5 percent by weight of lithium fluoride, and being further characterized by improved properties of forming lubricating solid-film.